Young Asian and Pacific Islander (API) men who have sex with men (MSM) are experiencing a double epidemic of HIV infection and drug use. Recent HIV incidence data indicate that almost two out of 100 API MSM aged 18-29 years (1.8%) are seroconverting every year. Close to half of these men (47%) engage in unprotected anal intercourse during a six-month period. Moreover, nearly two-thirds (63%) used illicit drugs in the past six months with methylenedioxymethamphetamine ("ecstasy") being the most popular drug of choice (47%). Research has shown that sex under the influence of substances is the most significant correlate of unprotected anal intercourse in API MSM. Our recent work with 18- to 29-year-old API MSM revealed that using ecstasy and inhalant nitrites during sex was associated with unprotected anal intercourse, whereas using marijuana, gamma-hydroxybutyrate, and crystal methamphetamine during sex was not. Nonetheless, few studies have focused on the intertwining nature of drug use and sexual behaviors that put young API MSM at high risk for HIV. We propose a two-year exploratory study (R21) as a first step to understanding the association between drug use and sexual risk among young API MSM (i.e., ages 18-29). Specifically, we will: explore subjective meanings and expectations about the effects of drug use on social interactions, inhibition, and sex (i.e., "drug expectancies"); characterize social networks (e.g., network member characteristics, norms, support) and explore their role in determining levels of drug use and sexual risk; identify "personal vulnerabilities" (e.g., experiences of social discrimination), sexual partnership characteristics (e.g., partner age and ethnicity), and social contexts (e.g., multiday MSM social gatherings) related to drug use during sexual activity; and explore possible pathways by which these five domains (e.g., drug expectancies, social networks, personal vulnerabilities, sexual partnerships, social contexts) link drug use with sexual risk among young API MSM. We will collect qualitative data in three phases: (1) 20 interviews with key informants knowledgeable about drug-using young API MSM and ethnographic mapping of venues frequented by these API men, (2) in-depth interviews with 60 drug-using young API MSM, and (3) focus group discussions with another 60 drug-using API MSM. These data will be used to help identify mechanisms linking drug use and sexual risk for HIV among young API MSM. The proposed study will generate in-depth knowledge to help develop a culturally appropriate model that can better explain the relationships between drug use and sexual risk among young API MSM. This study will also advance the field of HIV prevention research by investigating the contributions of social networks to drug use and sexual risk-taking, an area that has received little attention to date in studies of MSM.